Kyriakoula Marinou

Homocysteine and coronary atherosclerosis: from folate fortification to the recent clinical trials

Plasma total homocysteine (Hcy) has been associated with cardiovascular risk in multiple large-scale epidemiological studies, and it has been considered as an independent risk factor for atherosclerosis. Homocysteine lowering, achieved after the introduction of the folate food fortification programme in North America, was accompanied by an accelerated decline of cardiovascular risk and especially of stroke. Although the initial clinical trials suggested that homocysteine-lowering treatment with folates and B vitamins induces coronary plaque regression, this finding was not confirmed by more recent clinical studies. Under the light of the findings from the recent large randomized clinical trials that failed to document a benefit of Hcy lowering on clinical outcome of patients with atherosclerosis, the role of Hcy as a risk factor and the efficacy of Hcy lowering against atherosclerosis have been questioned. Therefore, better understanding of the mechanisms relating Hcy and Hcy-lowering treatment with vascular function and atherogenesis is crucial, to help us understand why clinical trials failed to show a benefit from Hcy-lowering treatment. Are these therapeutic strategies ineffective because they fail to reduce intracellular Hcy levels and vascular redox state or should Hcy stop being considered as an independent risk factor for atherosclerosis from now on? In this review article, we provide a global approach of the molecular mechanisms relating Hcy with cardiovascular risk and introduce possible mechanistic explanations regarding the inability of clinical trials to detect any clinical benefit from Hcy-lowering treatment in secondary prevention. Finally, we provide clinical recommendations regarding the therapeutic strategies targeting homocysteine in the general population.

Rapid, Direct Effects of Statin Treatment on Arterial Redox State and Nitric Oxide Bioavailability in Human Atherosclerosis via Tetrahydrobiopterin-Mediated Endothelial Nitric Oxide Synthase Coupling

Background— Treatment with statins improves clinical outcome, but the exact mechanisms of pleiotropic statin effects on vascular function in human atherosclerosis remain unclear. We examined the direct effects of atorvastatin on tetrahydrobiopterin-mediated endothelial nitric oxide (NO) synthase coupling in patients with coronary artery disease. Methods and Results— We first examined the association of statin treatment with vascular NO bioavailability and arterial superoxide (O2·−) in 492 patients undergoing coronary artery bypass graft surgery. Then, 42 statin-naïve patients undergoing elective coronary artery bypass graft surgery were randomized to atorvastatin 40 mg/d or placebo for 3 days before surgery to examine the impact of atorvastatin on endothelial function and O2·− generation in internal mammary arteries. Finally, segments of internal mammary arteries from 26 patients were used in ex vivo experiments to evaluate the statin-dependent mechanisms regulating the vascular redox state. Statin treatment was associated with improved vascular NO bioavailability and reduced O2·− generation in internal mammary arteries. Oral atorvastatin increased vascular tetrahydrobiopterin bioavailability and reduced basal and N-nitro-L-arginine methyl ester–inhibitable O2·− in internal mammary arteries independently of low-density lipoprotein lowering. In ex vivo experiments, atorvastatin rapidly improved vascular tetrahydrobiopterin bioavailability by upregulating GTP-cyclohydrolase I gene expression and activity, resulting in improved endothelial NO synthase coupling and reduced vascular O2·−. These effects were reversed by mevalonate, indicating a direct effect of vascular hydroxymethylglutaryl-coenzyme A reductase inhibition. Conclusions— This study demonstrates for the first time in humans the direct effects of statin treatment on the vascular wall, supporting the notion that this effect is independent of low-density lipoprotein lowering. Atorvastatin directly improves vascular NO bioavailability and reduces vascular O2·− through tetrahydrobiopterin-mediated endothelial NO synthase coupling. These findings provide new insights into the mechanisms mediating the beneficial vascular effects of statins in humans. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103.

Obesity and cardiovascular disease: From pathophysiology to risk stratification

Obesity is associated with numerous co-morbidities such as cardiovascular diseases (CVD), type 2 diabetes, hypertension and others. As obesity is considered to be a major risk factor for atherosclerosis, understanding of the underlying mechanisms leading to obesity and linking obesity with atherogenesis is necessary, for the development of therapeutic strategies against atherosclerosis. The pathophysiology of CVD linked to obesity is an area of intensive research. In this review we examine the role of obesity on CVD, and we focus on specific mechanisms of major importance in atherogenesis, such as the role of adipokines, insulin resistance, endothelial function and cardiac structure with emphasis on the effects of obesity on vascular endothelium and atherosclerosis. We then proceed from the pathophysiology of obesity to clinical practice, and we discuss clinical studies linking obesity with subclinical or overt CVD. We highlight that obesity is an easily assessed cardiovascular risk factor in the clinical setting and strategies to promote optimal body weight should be encouraged.

Preoperative Atorvastatin Treatment in CABG Patients Rapidly Improves Vein Graft Redox State by Inhibition of Rac1 and NADPH-Oxidase Activity

Background— Statins improve clinical outcome of patients with atherosclerosis, but their perioperative role in patients undergoing coronary artery bypass grafting (CABG) is unclear. We hypothesized that short-term treatment with atorvastatin before CABG would improve the redox state in saphenous vein grafts (SVGs), independently of low-density lipoprotein cholesterol (LDL)-lowering. Methods and Results— In a randomized, double-blind controlled trial, 42 statin-naïve patients undergoing elective CABG received atorvastatin 40 mg/d or placebo for 3 days before surgery. Circulating inflammatory markers and malondialdehyde (MDA) were measured before and after treatment. SVG segments were used to determine vascular superoxide (O2·−) and Rac1 activation. For ex vivo studies, SVG segments from 24 patients were incubated for 6 hours with atorvastatin 0, 5, or 50 &mgr;mol/L. Oral atorvastatin reduced vascular basal and NADPH-stimulated O2·− in SVGs (P<0.05 for all versus placebo) and reduced plasma MDA (P<0.05), independently of LDL-lowering and of changes in inflammatory markers. In SVGs exposed to atorvastatin ex vivo, without exposure to LDL, basal and NADPH-stimulated O2·− were significantly reduced (P<0.01 for both concentrations versus 0 &mgr;mol/L) in association with a striking reduction in Rac1 activation and 1 membrane-bound Rac1 and p67phox subunit. The antioxidant effects of atorvastatin were reversed by mevalonate, implying a dependence on vascular HMG-CoA reductase inhibition. Conclusions— Short-term treatment with atorvastatin 40 mg/d before CABG improves redox state in SVGs, by inhibiting vascular Rac1-mediated activation of NADPH-oxidase. These novel findings suggest that statin therapy should be maintained or initiated in patients undergoing CABG, independently of LDL levels. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103.

The role of adiponectin in human vascular physiology

Adiponectin (ApN) is an adipose tissue-derived hormone which is involved in a wide variety of physiological processes including energy metabolism, inflammation, and vascular physiology via actions on a broad spectrum of target organs including liver, skeletal muscle, and vascular endothelium. Besides possessing insulin sensitizing and anti-inflammatory properties ApN also exerts a pivotal role in vascular protection through activation of multiple intracellular signaling cascades. Enhancement of nitric oxide generation and attenuation of reactive oxygen species production in endothelial cells along with reduced vascular smooth muscle cell proliferation and migration constitute some of ApNs vasoprotective actions. Additionally, recent data indicate that ApN has direct myocardio-protective effects. Decreased plasma ApN levels are implicated in the pathogenesis of the metabolic syndrome and atherosclerosis and may serve as a diagnostic and prognostic biomarker as well as a rational pharmaco-therapeutic target to treat these disorders. This review article summarizes recent work on the cardiovascular actions of ApN.

Wnt signaling in cardiovascular physiology

Wnt signaling pathways play a key role in cardiac development, angiogenesis, and cardiac hypertrophy; emerging evidence suggests that they are also involved in the pathophysiology of atherosclerosis. Specifically, an important role for Wnts has been described in the regulation of endothelial inflammation, vascular calcification, and mesenchymal stem cell differentiation. Wnt signaling also induces monocyte adhesion to endothelial cells and is crucial for the regulation of vascular smooth-muscle cell (VSMC) behavior. We discuss how the Wnt pathways are implicated in vascular biology and outline the role of Wnt signaling in atherosclerosis. Dissecting Wnt pathways involved in atherogenesis and cardiovascular disease may provide crucial insights into novel mechanisms with therapeutic potential for atherosclerosis.

Myocardial Redox State Predicts In-Hospital Clinical Outcome After Cardiac Surgery Effects of Short-Term Pre-Operative Statin Treatment

OBJECTIVES The purpose of this study was to evaluate the role of the myocardial redox state in the development of in-hospital complications after cardiac surgery and the effect of statins on the myocardial redox state. BACKGROUND Statins improve clinical outcome after cardiac surgery, but it is unclear whether they exert their effects by modifying the myocardial redox state. METHODS We quantified myocardial superoxide anion (O(2)(-)) and peroxynitrite (ONOO(-)) and their enzymatic sources in samples of the right atrial appendage (RAA) from 303 patients undergoing cardiac surgery who were followed up until discharge, and in 42 patients who were randomized to receive 3-day treatment with atorvastatin 40 mg/d or placebo before surgery. The mechanisms by which atorvastatin modifies myocardial redox state were investigated in 26 RAA samples that were exposed to atorvastatin ex vivo. RESULTS Atrial O(2)(-) (derived mainly from nicotinamide adenine dinucleotide phosphate [NADPH] oxidases) and ONOO(-) were independently associated with increased risk of atrial fibrillation, the need for post-operative inotropic support, and the length of hospital stay. Pre-operative atorvastatin treatment suppressed atrial NADPH oxidase activity and myocardial O(2)(-) and ONOO(-) production. Ex vivo incubation of RAA samples with atorvastatin induced a mevalonate-reversible and Rac1-mediated inhibition of NADPH oxidase. CONCLUSIONS There is a strong independent association between myocardial O(2)(-)/ONOO(-) and in-hospital complications after cardiac surgery. Both myocardial O(2)(-) and ONOO(-) are reduced by pre-operative statin treatment, through a Rac1-mediated suppression of NADPH oxidase activity. These findings suggest that inhibition of myocardial NADPH oxidases may contribute to the beneficial effect of statins in patients undergoing cardiac surgery. (Effects of Atorvastatin on Endothelial Function, Vascular and Myocardial Redox State in High Cardiovascular Risk Patients; NCT01013103).

Effects of Ramipril on Endothelial Function and the Expression of Proinflammatory Cytokines and Adhesion Molecules in Young Normotensive Subjects With Successfully Repaired Coarctation of Aorta: A Randomized Cross-Over Study

OBJECTIVES The purpose of this study was to evaluate the effect of ramipril on endothelial function and inflammatory process in a group of normotensive subjects with successfully repaired coarctation of the aorta (SCR). BACKGROUND Subjects with SCR experience higher long-term cardiovascular risk as a result of the relapse of arterial hypertension or owing to nonreversible structural changes in the pre-coarctation arterial tree. These subjects experience endothelial dysfunction in the right forearm and appear to have elevated levels of proatherogenic inflammatory markers, even in the absence of arterial hypertension. METHODS Twenty young individuals age 27.3 +/- 2.4 years old with SCR 13.9 +/- 2.2 years previously, received ramipril 5 mg/day for 4 weeks in a randomized, cross-over, controlled trial. Endothelial function was evaluated in the right forearm by gauge-strain plethysmography, and serum levels of interleukin (IL)-1b, IL-6, soluble CD40 ligand (sCD40L), and soluble vascular cell adhesion molecule (sVCAM)-1 were determined by enzyme-linked immunosorbent assay. RESULTS Ramipril improved endothelial function (p < 0.001) and decreased the expression of proinflammatory cytokine IL-6 (p < 0.05) and sCD40L (p < 0.01). Furthermore, ramipril decreased serum levels of sVCAM-1 (p < 0.01) but failed to affect serum levels of C-reactive protein. These effects were independent of blood pressure lowering. CONCLUSIONS Ramipril reversed the impaired endothelial function and decreased the expression of proinflammatory cytokine IL-6, sCD40L, and adhesion molecules in normotensive subjects with SCR. These findings imply that ramipril treatment may have antiatherogenic effects in subjects with SCR, even in the absence of arterial hypertension.

Role of asymmetrical dimethylarginine in inflammation-induced endothelial dysfunction in human atherosclerosis.

We explored the role of asymmetrical dimethylarginine (ADMA) as a cause of endothelial dysfunction induced by systemic inflammation. In vitro data suggest that ADMA bioavailability is regulated by proinflammatory stimuli, but it is unclear whether ADMA is a link between inflammation and endothelial dysfunction in humans. In study 1 we recruited 351 patients with coronary artery disease (CAD) and 87 healthy controls. In study 2 we recruited 69 CAD, 69 healthy, and 10 patients with rheumatoid arthritis, whereas in study 3, 22 healthy and 70 CAD subjects were randomly assigned to Salmonella typhii vaccination (n=11 healthy and n=60 CAD) or placebo (n=11 healthy and n=10 CAD). Circulating interleukin 6/ADMA and flow-mediated dilation (FMD) were measured at 0 and 8 hours. In study 1, ADMA was inversely correlated with FMD in healthy individuals and CAD patients (P<0.0001 for both). However, interleukin 6 was inversely correlated with FMD (P<0.0001) in healthy subjects but not in CAD patients. The positive correlation between ADMA and interleukin 6 was stronger in healthy (r=0.515; P<0.0001) compared with CAD (r=0.289; P=0.0001) subjects. In study 2, both patients with rheumatoid arthritis and CAD had higher interleukin 6 (P<0.0001) and ADMA (P=0.004) but lower FMD (P=0.001) versus healthy subjects. In study 3, vaccination increased interleukin 6 in healthy (P<0.001) and CAD (P<0.001) subjects. FMD was reduced in healthy subjects (P<0.05), but its reduction in CAD was borderline. Vaccination increased ADMA only in healthy subjects (P<0.001). Systemic, low-grade inflammation leads to increased ADMA that may induce endothelial dysfunction. This study demonstrated that ADMA may be a link between inflammation and endothelial dysfunction in humans.

Structural and Functional Properties of Deep Abdominal Subcutaneous Adipose Tissue Explain Its Association With Insulin Resistance and Cardiovascular Risk in Men

OBJECTIVE Fat distribution is an important variable explaining metabolic heterogeneity of obesity. Abdominal subcutaneous adipose tissue (SAT) is divided by the Scarpa’s fascia into a deep subcutaneous adipose tissue (dSAT) and a superficial subcutaneous adipose tissue (sSAT) layer. This study sought to characterize functional differences between the two SAT layers to explore their relative contribution to metabolic traits and cardiovascular risk (CVR) profile. RESEARCH DESIGN AND METHODS We recruited 371 Caucasians consecutively from a local random, population-based screening project in Oxford and 25 Asian Indians from the local community. The depth of the SAT layers was determined by ultrasound (US), and adipose tissue (AT) biopsies were performed under US guidance in a subgroup of 43 Caucasians. Visceral adipose tissue (VAT) mass was quantified by dual-energy X-ray absorptiometry scan. RESULTS Male adiposity in both ethnic groups was characterized by a disproportionate expansion of dSAT, which was strongly correlated with VAT mass. dSAT depth was a strong predictor of global insulin resistance (IR; homeostatic model assessment of IR), liver-specific IR (insulin-like growth factor binding protein-1), and Framingham risk score independently of other measures of adiposity in men. Moreover, dSAT had higher expression of proinflammatory, lipogenic, and lipolytic genes and contained higher proportions of saturated fatty acids. There was increased proportion of small adipocytes in dSAT. CONCLUSIONS SAT is heterogeneous; dSAT expands disproportionally more than sSAT with increasing obesity in Caucasian males (confirmed also in Asian Indians). Its expansion is related to increased CVR independent of other adiposity measures, and it has biological properties suggestive of higher metabolic activity contributing to global IR.